Alignment of a shadow frame and large flat substrates on a heated support

ABSTRACT

Centering pins mounted to a susceptor in a vacuum chamber align a glass substrate with respect to the susceptor on which it is supported, and with respect to a shadow frame which overlies the periphery of the substrate and protects the edge and underside of the substrate from undesired processing. 
     Shaped pins loosely mounted in openings in the susceptor so that the pins extend above the upper surface of the susceptor support the centered glass substrate during the transporting stages, but recess into the heated susceptor during processing.

This is a continuation of U.S. application Ser. No. 08/462,442, filedJun. 5, 1995, now abandoned, which is a continuation of U.S. applicationSer. No. 08/313,501 filed Sep. 26, 1994, now abandoned, which is acontinuation of U.S. application Ser. No. 08/010,890 filed Jan. 28,1993, now U.S. Pat. No. 5,352,294.

This invention relates to a method of aligning a CVD deposition mask,herein called a shadow frame, and large glass substrates on a susceptoror heated support. More particularly, this invention relates toapparatus for carrying out the alignment and support of largerectangular glass substrates, for processing and automatic exchange ofthe substrates into and from a processing chamber.

BACKGROUND OF THE INVENTION

The semiconductor industry has been using single substrate (siliconwafer) processing chambers for some time because the chamber volume canbe minimized, contamination of the substrate has been reduced, processcontrol is increased and, therefore, yields are improved. Further,vacuum systems have been developed, such as described in Maydan et al,U.S. Pat. No. 4,951,601, that allow several sequential processing stepsto be carried out in a plurality of vacuum processing chambers connectedto a central transfer chamber, so that several processing steps can beperformed on a substrate without its leaving a vacuum environment. Thisfurther reduces the possibility of contamination of the substrates.

Recently the interest in providing large glass substrates with up to onemillion active thin film transistors thereon for applications such asactive matrix TV and computer displays has been heightened. These largeglass substrates, generally of a size up to about 350×450×1 mm, requirevacuum processing chambers for deposition of thin films thereon. Thebasic methods and processing chambers, e.g., plasma-enhanced chemicalvapor deposition (PECVD), PVD, etch chambers and the like, are similarto those used for depositing layers and patterning thin films on siliconwafers. A practicable system that can perform multiple process steps onglass substrates is disclosed by Turner et al (Ser. No. 08/010,684) in acopending application filed concurrently herewith entitled "VACUUMPROCESSING APPARATUS HAVING IMPROVED THROUGHPUT." However, because ofthe large size of the glass substrates, several problems have been notedin their handling and processing in vacuum processing chambers.

During processing, the edge and backside of the glass substrate must beprotected from deposition. Borrowing from the semiconductor processingart, a deposition-masking ring (or in this case, a rectangle) or shadowframe is placed about the periphery of the substrate to preventprocessing gases or plasma from reaching the edge and backside of thesubstrate in a CVD chamber for example. The susceptor, with a substratemounted thereon, can have a shadow frame which will surround and coverseveral millimeters of the periphery of the front surface of thesubstrate and this will prevent edge and backside deposition on thesubstrate. If however, the shadow frame is not properly centered withrespect to the substrate during processing, the amount of shadowing thatoccurs on each edge of the substrates will be unequal and unacceptable.

A factor complicating the alignment of the substrate to the susceptor isthe following. For proper set-up, calibration, and debugging of theautomated movement of a substrate into and out of a processing chamber,it is important to be able to execute these activities at roomtemperature. Therefore, the chamber components which provide support andalignment for the substrates must be sized and shaped to performsimilarly at room temperature as at normal operating temperature. Thesusceptor or support for the large glass substrate, generally made ofaluminum and which is heated resistively or otherwise, has a very largecoefficient of thermal expansion or CTE (about 22×10⁻⁶ /° C.) and thusincreases in size by 0.72% when heated from room temperature to aprocessing temperature of about 350° C. Since the type of glass ingeneral use in the flat panel display industry has a low CTE (4.6×10⁻⁶/° C.), the size of the glass increases in size only about 0.15% fromroom temperature to 350° C. Because of this difference, when the glassplate and susceptor are heated to elevated temperatures, there is asignificant difference in size between the glass and its susceptorsupport relative to the room temperature condition and it becomesdifficult to center or maintain alignment of the heated glass plate onthe susceptor. Again this contributes to non-uniformities in the amountof masking occurring along each edge plates and to unacceptablevariations in the location of the deposition zone on the glass plate.

Therefore a means of centering a large glass substrate with respect toits susceptor support and to a shadow frame has been sought.

SUMMARY OF THE INVENTION

A centering pin assembly is mechanically registered to the center of thesusceptor but independently movable to ensure bothtemperature-independent centering of a large glass substrate withrespect to a heated susceptor and centering of a shadow frame withrespect to the substrate. The shadow frame is shaped so as to mate withthe centering pins, thereby also aligning the shadow frame with respectto the substrate.

Shaped support pins are loosely held in the susceptor by their ownweight and are guided by closely fitting mating holes. These pinsprovide support for the large glass substrates during automatic exchangeof the substrate and protect the susceptor from damage during periodicdry-etch cleaning cycles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a first embodiment of a centering pin of theinvention.

FIG. 2 is a cross-sectional side view of one side of the shadow frame ofthe invention.

FIG. 3 is a cross-sectional view of a single substrate chemical vapordeposition (CVD) vacuum chamber for processing large glass substrates inwhich the centering pin assembly and shadow frame of the invention canbe used.

FIG. 4, 5, and 6 are three cross-sectional side views of a centering pinand its support plate, a shaped support pin, one side shadow frame, aglass substrate, the susceptor/heated support and the chamber body. Theviews show all of these components in their relationships to one anotherin the three principal positions of the active components.

FIG. 7 is a side view of a shaped support pin of the invention.

FIG. 8 is a side view and FIG. 9 is a top view of a centering pinassembly.

FIG. 10 is a side view of a second embodiment of the centering pin.

FIG. 11 is a three-dimensional view of a third embodiment of thecentering pin.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a centering pin 12 of the invention has a topsurface 20 which supports a shadow frame 40 of FIG. 2 and has extendingvertically from it a triangular finger 14. The finger 14 has a first,outer edge 16 sloping in one direction that mates with and centers theshadow frame 40 with respect to the centering pin assembly 220 of FIG.8. It further has a second, inner edge 18 sloping in another directionthat, if necessary, centers a glass substrate 108 disposed on its innerside before the substrate 108 comes into contact with the susceptor 113during a loading sequence.

FIG. 2 is a cross-sectional view of a shadow frame 40 useful herein. Theshadow frame 40 comprises an upper surface 42 with a lip 44 extendinghorizontally therefrom which is to overlie the periphery of the glasssubstrate 108 to thereby protect the edge and bottom of the substrate108 from depositions. A tapered side 46 mates with the outer slopingside 16 of the centering pin 12. The shadow frame 40 in this embodimentis either ceramic or anodized aluminum, but can be made of a number ofother suitable materials.

Under normal circumstances, as illustrated in FIG. 4, when a robot blade230 is inserted into a chamber with a substrate 108 atop it to load intothe chamber for processing, the position of the substrate 108 is properand located precisely enough that no centering is necessary. But in theevent that some mispositioning of the substrate 108 occurs which iswithin the "capture window" created by the inner sloping sides 18 of twoopposing centering pins 12, the substrate 108 will be centered by thesubstrate being guided down the slope(s) 18 of the centering pin(s) 12as the centering pin assembly 220 moves vertically upward and lifts thesubstrate 108 from the robot blade 230. An obviously similar descriptionof the function of sloping sides 16 of the centering pins 12 applies tothe establishment and maintenance of the centered condition of theshadow frame 40 when, moving upward, the centering pin assembly 220reaches the "lift" position shown in FIG. 5. The realignment of thesubstrate 108 and the alignment of the shadow frame 40 to the substrate108 is passive, being gravitationally effected by the interaction ofthese parts with the centering pins 12.

The substrate 108 and the shadow frame 40 are thus aligned to each otherand centered on the susceptor 113 by the single component, the centeringpin assembly 220. This alignment is a translational alignment in boththe x- and y-axes of the plane of a substrate 108 and the plane of theshadow frame 40; and it is rotational alignment about their z-axes as aresult of using four pairs of opposing centering pins 12, as illustratedin plan view in FIG. 9, which are located to act near the corners of asubstrate 108 and the shadow frame 40 FIG. 9 shows how the centeringpins 12 are arranged in four opposing pairs (8 pins total) in order toprovide centering translationally and rotationally for the rectangularsubstrate 108 and the shadow frame 40.

The centering pin assembly 220 and most importantly the pin supportplate 122 are made of a material having a low coefficient of thermalexpansion (CTE). In this embodiment it is alumina, which ires a CET ofabout 7.4×10⁻⁶ /° C. and therefore exhibits a dimensional change similarto that of the glass substrate 108 of only about 0.24% from roomtemperature to processing temperatures of about 350° C.

FIG. 3 is a cross-sectional view of a single-substrate CVD processingchamber useful for depositing thin films onto large glass substrates andin which the novel centering pin assembly and shadow frame are used.

A vacuum chamber 120 comprises a chamber body 102 and a lid 103 attachedby a hinge to the body 102. A gas dispersion plate 104 having aplurality of openings 106 therein for the distribution of reaction gasesis mounted in the lid 103. The shadow frame 40 is supported by a ledge110 on the inner surface 112 of the wall 102 during the time that thesubstrate 108 is entering or exiting the chamber 120 through an entry126. The susceptor/heated support 113, mounted on ceramic support 114,can be moved up and down by a shaft 118 in conventional manner. Asshown, the susceptor 113 is between its down or loading/unloadingposition of FIG. 4 and the lift position of FIG. 5. The susceptor 113supports the substrate 108 to be processed on its upper surface 116 whenit is in its up processing position of FIG. 6.

A plurality of centering pins 12 rigidly mounted on the separate pinsupport 122 make up the centering pin assembly 220 of FIG. 9. Thisassembly is also movable up and down by the shaft 118 but is separatelymounted on an outer shaft 124. For example, a guiding bearing on thesusceptor shaft 118 allows the centering pin assembly 220 and thesusceptor support 114 to be separately movable. The positions of thecentering pins 12 are fixed with respect to their support 122 so thatthe glass substrate 108 to be processed will be centered with respect tothe centering pins 12. The pin support 122 is located below thesusceptor 113 and its support 114, and the centering pins 12 passthrough holes in these parts.

FIG. 7 shows a shaped support pin 200, a plurality of which are used tosupport the substrate 108 during loading and unloading of the substrateonto and off from the robot blade 230. These pins 200 are floating undertheir own weight in the susceptor 113 and are forced by contact at theirbottom with the centering pin support 122 to protrude through thesusceptor 113 when the susceptor is in the lift position of FIG. 5 orthe load position of FIG. 4. Because the component(s) (in thisembodiment, the shaped pins) which lift the substrate 108 from thesusceptor 113 must be beneath the substrate, (an) access hole(s) 117must penetrate the susceptor 113 and its support 114 to allow thelifting device(s) through. However, if the hole is not covered beneaththe substrate 108, several deleterious effects can occur including lossof temperature control at that spot on the substrate, and, in the caseof plasma enhanced deposition or etch clean process, the discharge isgreatly enhanced which is produced at such discontinuities as a hole inthe surface 116 creates. Subsequent thermal or sputtering damage to thehole surfaces can result. Therefore the shaped support pins 200 aredesigned to float within the susceptor and be carried with the susceptor113 as it moves above the lift position of FIG. 5 into the processposition of FIG. 6. The top of the shaped support pin 200 has a taperedbottom surface 205 which fits tightly inside a mating tapered surface115 in the susceptor 113, which thereby effectively seals the hole 117in the susceptor 113. The shaped support pin 200 is then suspended inthe susceptor 113 by the fit of support pin surface 205 inside susceptorsurface 115 when the susceptor is in the process position of FIG. 6. Inthis position, the top surfaces 202 of the shaped support pin 200 shouldbe either flush with or slightly under flush with the top susceptorsurface 116.

The substrate load sequence is as follows. A glass substrate 108supported by a robot blade 230 enters the vacuum chamber 120 through theentry port 126 while the susceptor 113 and centering pin assembly 220are in the down position of FIG. 4. The shaped pins 200 contact at theirlower ends the pin support plate 122 and their top surfaces 202 aregenerally horizontally aligned with the bottom of the inner slopingedges 18 of the centering pins 12. The centering pins 12 are raised upto support and if necessary center the glass substrate 108 with respectto the susceptor 113. In moving to the lift position of FIG. 5, theglass substrate 108 is centered by the sloping sides 18 of the centeringpins and supported by the top surfaces 202 of the shaped pins 200protruding above the susceptor 113. The robot blade 230 is withdrawn,and the entry port 126 is closed. The centering pin assembly 220continues to move upwards along with the shaped support pins 200 untilthe edges 18 of the centering pins 12 contact the tapered sides 46 ofthe shadow frame 40. The shadow frame 40 is at once lifted upwardly awayfrom the ledge 110 of the wall 102 and centered with respect to theshadow frame 40 and the substrate 108. The shadow frame 40 is therebycentered, if needed, and supported in its centered position as thecentering pin assembly 220 is raised together with the susceptor 113into the lift position of FIG. 5. At this point in the vertical motion,the centering pin assembly 220 reaches a stop and does not rise anyhigher. The susceptor 113 is now raised until it supports the glassplate 108 and the lip 44 of the shadow frame 40, so that the shadowframe 40 is now supported solely by the substrate 108. At this point,the shaped pins 200 are lifted off the pin support plate 122 by therising susceptor 113 and become flush with the top susceptor surface116. The final processing position of the glass substrate and the shadowframe is shown by means of dotted lines at 108A and 40A in FIG. 3 and indetail in FIG. 6. Since the glass substrate 108 and the shadow frame 40can be made to have similar coefficients of thermal expansion, theirrelative size does not change with respect to each other duringprocessing and the shadow frame 40 remains centered with respect to thesubstrate 108.

The reactant gases are fed through the gas dispersion plate 104 andprocessing is completed. The susceptor 113, the substrate 108 and theshadow frame 40 are then lowered to the lift position of FIG. 5, whereatthe robot blade 230 is inserted. The susceptor 113 and centering pinassembly 220 then are lowered together. The substrate 108 deposited onthe robot blade and the processed glass substrate can be removed fromthe chamber 120.

A simpler but less preferred embodiment of the invention is illustratedin FIG. 10. When the robot arm 230 places the substrate 108 within thechamber, the sloping inner sidewalls 18 center the substrate 108 as thecentering assembly 220 is raised. The centered substrate 108 rests oninner, horizontally extending ledges 19 of the centering pins 12 beforethe susceptor 113 lifts the substrate 108 from the inner ledges 19 toengage and lift the shadow frame 40 from the centering pins 12. Theembodiment of FIG. 10 does not require the shaped pins 200 because theinner ledges 19 perform the substrate-support function of the shapedpins 200, as shown in FIG. 5. However, the holes 117 in the susceptor113 which allow the centering pins 12 to pass through must extendcorrespondingly further toward the center of the susceptor 113, andtherefore the frame lip 44 must be longer if it is to cover the largerhole in the susceptor 113. The longer lip 44 however has the undesirableeffect of reducing the usable processed area of the glass 108, and, aspreviously described, the uncovered hole can have deleterious effects onthe substrate 108 or the susceptor 113.

A third embodiment of the invention is illustrated in three dimensionsin FIG. 11. Four corner pins 212 rise from the four corners of the pinsupport plate 122. The intervening susceptor in not illustrated. Twoperpendicular triangular wedges 213 and 214 rise from a flat surface 215at the top of the corner pins 212. The substrate 108 is centered at itscorners 216 by the inner sloping surfaces 217 of the wedges 213 and 214,and its corners 216 are supported by the inner portions of the top pinsurface 215. The masking frame 40 is centered by the outer slopingsurfaces 218 of the corner pins 212 and i supported by the outerportions of the top pin surfaces 215. Four such corner pins 212 performthe same functions as four pairs of centering pins 12 of FIG. 10.

Although the invention is described herein in terms of certain specificembodiments, the centering pins, shadow frame and support pins can beemployed in apparatus other than CVD chambers and various materials andchamber pans may be substituted as will be known to one skilled in theart. The invention is meant to be limited only by the scope of theappended claims.

What is claimed is:
 1. A substrate processing system comprising:a) aprocessing chamber for processing a substrate inserted therein upon ablade horizontally movable into a processing area of said chamber; b) avertically movable centering support; c) a plurality of centeringmembers attached to said support and extending vertically therefrom,each said centering member havingi) an inner vertically extending side,and ii) a centering feature disposed on a top of said centering memberand having an inner inclined surface extending inwardly and downwardlyto said vertically extending side; and d) a substrate support verticallymovable with respect to said centering support for supporting saidsubstrate centered by said centering features.
 2. A substrate processingsystem according to claim 1 wherein each said centering feature furthercomprises an outer inclined surface extending downward and outwardlyfrom said inner inclined surface; andwherein said system furthercomprises a frame having an inwardly extending lip engageable with aperiphery of said substrate and having at least one inclined surfaceextending downwardly and outwardly from said lip, and slidingly engagingsaid outer inclined surface of said centering feature.
 3. A substrateprocessing system according to claim 1 further comprising a plurality ofsupport members vertically slidable in said substrate support, havinglower ends engageable with said centering support, and having a lengthsuch that, when their lower ends engage said centering support, uppersupport surfaces thereof receive and support said substrate centered bysaid centering features.
 4. A substrate process system according toclaim 3 wherein said support members have heads wherein said uppersupport surfaces are larger than the diameter of the lower ends thereofand wherein said substrate support member has recesses to receive saidheads without protruding therefrom.